Leaf type or blade type mechanical shutters have been used to regulate the amount of light that is going to reach the imaging areas of a filmstrip contained within a camera. Typically, the leaf type of shutter is an array of metal "blades" that are pivoted so that they all swing towards or away from the lens aperture of the camera. When the shutter is closed, all the blades are overlapping in the center of the lens aperture and no light reaches the filmstrip. To open the shutter, the blades pivot away from the center of the aperture, so that light may pass through the aperture and expose the filmstrip. Sometimes leaf type mechanical shutters may have one or more blades, each of which may have a different diameter opening. When a picture is taken the blade or blades swing away from the center of the lens aperture so that light may pass through the aperture, through the blade or blade openings to expose the filmstrip. If a picture is not being taken, the shutter will be closed. The power to open and close the leaf type mechanical shutters is provided by a spring or springs that are under tension and the timing is controlled by a watch-type gear train.
Electromagnetic actuated leaf type shutters have been developed to reduce the amount of energy that is required to open and close leaf type mechanical shutters. Electromagnetic shutters are faster than mechanical shutters from 4 mm diameter to 20 mm diameter aperture openings and electromagnetic shutters may be controlled with greater accuracy than mechanical shutters. Thus, electromagnetic shutters have higher performance characteristics, than leaf type mechanical shutters.
A typical two blade leaf style shutter may use gearing to actuate the two blades, or one blade could have a pin, while the other blade has a slot for their actuation. Shutters with more than two blades typically have a synchronizing mechanism that actuate all the shutter blades at the same time. Gearing or pins in slots, that are connected to the shutter blades and the synchronizing mechanism, may be used to interface the synchronizing mechanism to the shutter blades.
The inertia of the shutter mechanism is based upon the inertia's of the individual components of the shutter. Synchronizing rings that use gearing, have to be made sufficiently thick to ensure that the gears will always mate properly.
Synchronizing rings incorporating pins in slots have to be made sufficiently thick to allow for the pin to be held straight and rigid.
Even though the thickness and inertia of the synchronizing ring may be decreased, the synchronizing ring will still exhibit sliding friction, which degrades the performance of the shutter.
The three factors that affect a shutters performance are: clearance; inertia; and friction between individual components. The clearance of a shutter refers to gear backlash or extra space in the slot of a shutter blade that is used to prevent binding of the mating components. The inertia of a shutter refers to the relationship of the mass and velocity of the individual shutter components. The friction of a shutter refers to a force that opposes movement of two bodies that are in contact.
The problem with gearing in shutters is gear backlash. Gear backlash allows the gears to over rotate in the opening direction when the coupling mechanism i.e., synchronization gear is attempting to close the shutter. Gear backlash also allows the gears to over rotate in the closing direction when the coupling mechanism i.e., synchronization gear is attempting to open the shutter. Thus, the shutter blades over shoot the aperture and cause inaccurate exposures.
When pins are placed in the slots of shutter blades, the slots have built in clearance to prevent binding of the pin in the slot of the shutter blade. The clearance provided to prevent binding, has the same effect as gear backlash. The pins in the slots of the shutter blades over rotate in the opening direction while the coupling mechanism i.e. synchronization is attempting to close the shutter blades. The aforementioned gearing and pins in the shutter blades slots, reduce the control the control mechanism has on the shutter.